I know someone who has a commercially made fish cat bed.
[ame="http://www.amazon.com/Vo-Toys-Anglerfish-Cat-Tunnel-Plush/dp/B004UR8DJE/ref=sr_1_1?s=pet-supplies&ie=UTF8&qid=1327108186&sr=1-1"]Amazon.com: Vo-Toys Anglerfish Cat Tunnel Plush Cat Toy: Pet Supplies@@AMEPARAM@@http://ecx.images-amazon.com/images/I/414lHU2mp3L.@@AMEPARAM@@414lHU2mp3L[/ame]
There's an exit at the back of the fish under the tail. I intend to modify mine so they can get out the back. Our cats hate feeling trapped. I might see if I can leave some slots open at the bottom too, so they can stick their paws out to play with stuff. They like that.

I want to do the cat cabin in some kind of woodsy print. I really don't like all the bright neon colors that clash with everything else in our house.

Our current cat tent uses some kind of flexible wires for supports. It's the pop up style. They also have some of those $4 cubes from Walmart.